Irrigation sprinklers of the impact arm type, as for example, the sprinklers shown in U.S. Pat. Nos. 3,743,183 and 4,055,304, are extensively used. However, each sprinkler of this type known hitherto leaves a large annular area which is much dryer than the rest of the circle being sprinkled. The impact arm breaks up the stream of the sprinkler to provide better close-in coverage, but there still remains very poor coverage of the intermediate area.